Switched digital service ("SDS") telecommunication channels typically have either a 56 or 64 kilobit per second ("kb/s") data rate capacity. This data capacity being determined by the particular environment in which the channel is employed: a standard SDS network, or an Integrated Services Digital Network ("ISDN"). One method of performing data transmissions over a public telecommunication network at rates beyond the standard digital channel capacity is to simultaneously establish connections over multiple SDS channels. For example, if a sender wished to transmit data at a rate N times the standard digital channel data rate, it would be necessary to dial N telephone numbers, whereby establishing the N individual channel connections to N separate receivers on the premises of the intended recipient.
Since each of the individual digital channel connections was established by dialing a separate telephone number, differential path delays will likely exist among the channels. These differential delays arise as a result of dissimilar inter-channel switching, as well as differences in the length of the physical path traversed by each individual connection. Typical network routing practice dictates that the preferred route for a given connection from point A to point B is likely to change from moment to moment as a function of the instantaneous load on the network. As a result, even sequentially dialed calls from point A to point B may not be sent over the same physical path. The caller's inability to specify the particular physical path over which a given channel connection is effected almost guarantees differential delays will exist. To compensate for inter-channel delay differences, the recipient of the multiple calls must introduce a specific delay to each individual channel in order to synchronize the incoming signals. This compensation requires additional on-premises equipment, and a time consuming calibration process to determine the relative path delays among the channels.
An alternative to the communication method described above is to effect the multiple digital channel connections over a network configured so as to guarantee identical path lengths for all of the channels involve. While the capability to selectively restrict multiple digital channel connections to the same transmission path is available within some specialized telecommunication networks, most public telecommunication networks do not offer this function. Furthermore, reconfiguring existing network switches so that they are capable of securing, on-demand, multiple digital channel connections having equal path lengths would be quite costly, requiring a significant investment of both equipment and engineering.
Even within networks having a tandem architecture, wherein all communications between subscribers are restricted to routes traversing a particular switch (designated the tandem switch as it serves to link two other network switches), on-demand, multiple digital channel connections having equal path lengths cannot be reliably secured. This is due to the likelihood that the routing of all the channel connections involved would not be effected via the same network switches or facility routes outside of the tandem switch.